It is nutritionally and organoleptically desirable to provide fruits and fruit pieces in packaged dry food products such as cookie mixes, muffin mixes, pancake mixes, cereal bars, and packaged ready-to-eat cereals, for example. However, such products, and typically ready-to-eat cereal products, being dry and having relatively low water activities, naturally tend to further desiccate the dry fruit. Hence, after a short time, untreated dried fruit, for example, dried apples, bananas, currants, dates, peaches, prunes, etc. and of course, raisins, and mixtures thereof, tend to become unacceptably hard, or at least to become quite tough when packaged in the presence of such dry products. Use of edible humectants such as glycerol to maintain the dried fruit in a softer, more desirable condition, has been widely reported.
Over 50 years ago, for example, John B. Segur et. al. received U.S. Pat. No. 1,853,151 which related to the topical application of glycerine to raisins. The Segur Patent taught, for example:
"Drying out of the fruits will occur and renders them harder and tougher.(Col. 1, lines 16-18.) PA1 "In the preferred embodiment of the invention, a coating of glycerol is applied superficially to the fruit which has been prepared for marketing in the usual manner and by common practices. This application may be effected by spraying the dried fruit with glycerol or an aqueous solution containing glycerol, or by immersing the fruits in glycerol or an aqueous solution containing glycerol. The quantity of glycerol applied may vary within wide limits, but for practical purposes will ordinarily not exceed 2 or 3% of the weight of the fruit, and in general will exceed 0.25%. For example, the dried fruit (prunes, for example) in suitable perforated trays or wire baskets or on a belt or perforated conveyor, is sprayed with about 0.75% of its weight of 95% glycerol, to produce a substantially uniform coating of glycerol thereon. (See column 2, lines 66-86.) (Emphasis added.) PA1 Spray application is ordinarily desirable because of its ready adaptability to either manual or mechanical operation. If desired, however, the dried fruit may be immersed in glycerol . . . Prolonged immersion is not required, as only superficial wetting of the surfaces of the fruit is desired. Thus, when the fruits are coated by immersion, it is ordinarily sufficient to immerse them (in perforated containers or wire baskets) in the liquid and immediately remove them.(Column 2, line 96. to col. 3, line 9) (". . . " indicates a portion omitted.) PA1 "The termination of the last stage of dehydration may, on the other hand, be characterized by the continued presence of the circulating liquid about and over the food. In such a case, restoration of normal pressure serves to drive the liquid into the cells and pores of the food. The result is the full cell impregnation of the food. (Col. 2, lines 31 to 38)
The Segur Patent goes on to teach:
Immersing fruit such as raisins in glycerol as a means of both drying and infusing the fruit with such a humectant is also disclosed in a number of other patents and literature articles, such as the following.
U.S. Pat. No. 2,283,302, which issued in 1942 to W. A. Webb, teaches immersing raisins in an edible liquid such as glycerine or other specified liquids. In a preferred process, the Webb patent teaches the partial dehydration of the fruit, and subsequent impregnation with liquid glycerine, while it is immersed in the heated glycerine medium. The Webb Patent goes on to teach:
U.S. Pat. No. 3,952,112, which issued in 1976 to C. V. Fulger et al. (and for which reexamination certificate B1 3,952,112 issued on Oct. 8, 1985) also relates to the immersion i.e. static soaking of raisins in glycerine. Mr. Fulger also received U.S. Pat. No. 4,130,035 which relates to pretreating the raisins with alkali or hot weak acid to enhance the penetration of the glycerol.
U.S. Pat. No. 4,696,824, which issued on Sept. 29, 1987 to Meczkowski et al. also teaches coating raisins with glycerine followed by a coating of oil.
Numerous other patents relate to the application of coatings of many kinds to serve as a moisture barrier for the raisins.
One of the major undesirable aspects associated with the immersion of raisins in glycerol, is the fact that the raisin-skin transport phenomena is a two way street. The glycerol in which the raisins is immersed soon becomes diluted with components which come out from the raisins. Sugars, water, and other components are the principle diluents. Some food processors regard the resulting diluted glycerol solution of such components as being of sufficiently changed composition as to be unsuitable for extended immersion or repeated immersion of raisins, and the resulting decanted liquid glycerol solution becomes a disposal problem. This is not only a problem from the economic perspective, in view of all the wasted glycerol, but is also a problem from the environmental perspective, inasmuch as the waste material has a high biological oxygen demand (BOD).
Hence, it has long been understood that for the purpose of admixing it with a dry food, such as ready-to-eat cereal, for example, which inherently has a relatively low Water Activity, fruit could be pretreated to provide internal humectant to maintain its softness. However, the prior art has not appreciated just how high the internal humectant levels have to be in raisins, for example, in order to maintain good properties in prolonged sealed storage, especially in cereals having very low Water Activities, e.g. 0.3 or less, especially 0.2 or less.
We have recently discovered that in prolonged storage in ready to eat cereals having very low Water Activities, e.g. 0.3 or less, the level of glycerol infused into the raisins, for example, should be above about 15% by weight, based on the weight of the glycerol infused product, in order for the product to maintain its softness after storage in a container. This is vastly higher than the levels reported previously in the literature, to our knowledge.
On the other hand, we have discovered that the maximum amount of glycerol which can be applied to the surface of raisins, under simple topical application procedure, such as be spraying, or immersing in excess humectant and then removing the raisins from the glycerol, is about 13.8%. This falls short of the minimum amounts believed necessary to maintain softness in prolonged storage, in very low Water Activity dry food products, such as very low Water Activity ready-to-eat cereals.
It would be highly desirable to provide a process for manufacturing fruit having high levels of infused humectant such as glycerol, which process does not inherently result in the generation of a waste glycerol stream.
It would be highly desirable to provide the art with a procedure for infusing glycerol into raisins to result in internal levels of 14% or more, which procedure utilizes only topical or surface application of the glycerol.
It would also be highly desirable to provide dry food products such as ready to use mixes, and ready-to-eat cereals, preferably ready-to-eat cereals having a very low Water Activity (e.g. 0.3 or less ), having fruits such as raisins which do not become hard or tough on normal storage in the food package.